According to one aspect of the invention, there is provided a power take off device for an endless conveyor belt system of the type comprising an endless belt having an upper conveyor run for transporting material and a lower return run, the power take off device comprising an hydraulic pump operably linked to the belt or to a rotating component forming part of the conveyor belt system so as to generate hydraulic fluid at pressure only when the conveyor belt is in motion.
In another aspect, the invention provides a conveyor belt system incorporating a power take off device as defined above.
For convenience hereinafter an endless conveyor system will be referred to as a conveyor belt, or a conveyor belt system.
An existing roller or drum in the conveyor belt system can be utilised to provide rotary motion to drive an hydraulic pump, or a roller can be introduced into the conveyor belt system to achieve the required drive to the pump. The existing roller or the drive obtained from other components, or the introduced roller, becomes an automatically interlocked prime mover to rotate an hydraulic pump. Fluid pressure from the pump may then be used to power hydraulic actuators. Electrical motors, switchgear and interlocking supply would not be required.
Specifically the pump may be used to transmit a volume of fluid at pressure to a number of devices used on conveyor belts. These include belt scrapers, drum scrapers, top and bottom belt ploughs, rotary brush cleaners and fines conveyors.
In all these devices, as they are used, wear takes place and regular adjustments is required. Belt cleaning devices they need to be maintained in contact with the belt surface to ensure that efficient cleaning is taking place. By providing hydraulic fluid at pressure to actuators the cleaners can be maintained at constant pressure against the belt surface thereby providing a self adjusting mechanism at a pre-determined constant force which will require no adjustment throughout the cleaning elements' life.
The power take off of the invention is of particular utility for the automatic tensioning of belt cleaning devices, especially belt scrapers.
The hydraulic pump may have an internal or external relief valve, internal or external flow control, and an internal or external reservoir, or may be a pump that is contained within a roller, the inside of the roller being used as the reservoir. A support or bracket may fix the hydraulic pump to the conveyor framework and contain any torque reaction.
A driving roller may be introduced into the conveyor system to frictionally engage with any surface or edge of the belt fabric, or drums, to produce rotary motion or linear motion with which to rotate or otherwise drive the pump. Alternatively a stub shaft or drive train may be used to derive the necessary motion to the pump from existing roller, drums, or other rotary components within the endless belt system, or from any other components or equipment retrofitted to operate on the conveyor belt system. In another embodiment a roller may be introduced into the system which when the belt is not loaded with material is disengaged and frictional engagement takes place when the weight of the material being transported depresses the belt to rotate the pump roller.
The pump may be connected to the rotary motion or linear motion of the endless belt system by any suitable means, eg freewheel clutch, flexible drive cable, magnetic coupling or drive train. Rotary or linear actuators which are supplied with fluid pressure via hoses or pipes may be single or double acting.
The generating pump can take any suitable form, eg piston, gear, vane, centrifugal or diaphragm to generate the required hydraulic flow and pressure. Alternatively an existing pump may be used to provide the pressure such as a lubrication pump inside a gearbox. The pressure may be obtained by utilising the pressure generated by a scoop type traction coupling, to maintain constant pressure via a pressure reducing valve to belt cleaning equipment or any equipment that needs to be continually adjusted. The hydraulic fluid can be of any type or viscosity, eg mineral or vegetable oil, synthetic oil, soluble oil, water, detergent, cleaning fluid or disinfectant.
The device is fixed to any suitable of the conveyor by any suitable means and may be portable and attached to any suitable structure anywhere along its run to provide hydraulic pressure to operate pumps and hand tools, or to spray fluid onto the belt to clean or sterilise the belt.
The pump may be used to detect slowing down of the belt ie belt slip or overloading, whereby a pressure drop causes the power to be removed from the conveyor drive by the used of a pressure switch. The pressure generated may be used to maintain constant pressure to a belt scraper/cleaner and also to operate a vibrator attached to the scraper/cleaner to induce vibration forces into a localised area of the belt surface.
The power take off device may generate hydraulic fluid at pressure to more than one item of equipment by the use of unloading valves, direction valve, pressure reducing valves and the like. The power take off device may convert the rotary motion of the conveyor belt or other components within the conveyor system, or retrofitted to the conveyor system, into linear motion to drive an hydraulic pump that operates by linear motion.
The hydraulic fluid generated may power an automatic lubrication system to grease or oil at desired intervals, bearings and other moving components within and around the conveyor belt system.
The pump may be a tandem or triple pump within the same housing and driven from one source, producing fluid at pressure at different settings to operate more than one circuit.
The power take off device may provide hydraulic pressure to any number of belt cleaning devices.
The hydraulic pressure to the actuators may be removed when a joint in the belt is approaching allowing the cleaning device to relax from the belt and the joint to pass over the cleaner unhindered. Pressure would then be reapplied after the joint or obstruction has passed.
A pump may be fitted at each end of the conveyor and between drive input and pump a freewheel clutch may be fitted to ensure that pressure is only generated in one direction.
Fines conveyors are fitted underneath the drivehead of an endless conveyor to transfer spillage and debris removed from the belt surface by the aforementioned belt cleaners. These are usually of the type that has an endless chain with flight bars running in a race within the conveyor pan to convey material into the main chute along with the main flow of material. These chains stretch and wear takes place between the links. This slack chain needs to be continually adjusted to avoid the links standing on end and jamming in the return race. By fitting linear actuators at one end of the chain conveyor, with pressure being provided from a pump attached to the conveyor belt system, the slack chain could be continually adjusted at a predetermined force therefore negating any manual adjustment until the chain is worn or stretched beyond practical use.
The aforementioned uses only require the hydraulic power when the conveyor belt is in motion, once the conveyor belt has stopped the pressure in the hydraulic circuit reduces, relaxing the device it is operating. In most cases this would not be detrimental and probably advantageous as components in the system would not be under load when the conveyor belt is stationary. This relaxing of the component being operated would dislodge any material built up around the operating mechanism and not allow cylinders to stick in a position. Should it be required to maintain pressure in the circuit when the belt is stationary, a simple non-return valve would provide this feature.
The pressure and volume of fluid required to operate these devices would be very low by hydraulic standards. Small pumps operating at slow rpm would provide sufficient fluid at pressure without the need of a large reservoir. The amount of wear taking place on the cleaning elements can be measured in thousands of a millimeter per hour, therefore very little volume of oil is required, and is largely a case of maintaining a constant pressure to the actuators. Because of the low pressure and volume requirement, very little heat would be generated and power absorbed by the pump would also be small. Large diameter drums in the conveyor belt system would be ideal to use as the prime mover for the pump due to their low revolutions. The pump would be rotating slowly (in the order of 50 to 100 rpm) which would prolong the life of the pump and generate less heat, ensuring reliability.
The aforementioned used for this power take off can readily be adapted to existing cleaning systems which are generally manually adjusted. Belt cleaning devices need to be continually adjusted to maintain the required cleaning pressure. Every person will have a different setting that they think is correct but often is not. The use of this proposed system would allow the use of a given pressure to set the cleaner for a particular situation and once set would not require further adjustment until the cleaner element is worn out, reducing adjustment/maintenance requirement and operator error.
On reversing conveyors material is transported in both directions. A belt cleaner is fitted at each end of the conveyor belt system but each cleaner is only required to be in operation 50% of the time, but both are always in contact with the belt surface. The cleaner at the return end of the conveyor wears itself more than is necessary. By utilising a freewheel or one way clutch between the drive and the pump at each end of the conveyor, pressure will only be generated in one direction. When in motion the pump at the delivery end pressurises the scraper, whilst the scraper at the return end is relaxed as pressure is not being generated. Whichever direction the belt is running, the return end scraper is relaxed from the surface, prolonging the life of the belt surface and the life of the scraper element.
Generally, cleaning devices for conveyor belts are manually adjusted or adjusted by counterweights, rubber torsion units or springs. These adjusting methods do not provide constant cleaning pressure nor do they provide total self adjustment throughout the cleaner's life. For any belt cleaner to be successful its most important feature will be its ability to self adjust to compensate for element or blade wear whilst maintaining a constant pre-determined force against the belt.
Compressed air actuators charged from a ring main can be used to provide this self adjusting feature, but compressed air is not always available or financially viable. In remote locations away from a plant's main activity it would be costly to pipe air over long distances. It is this type of location where a self contained power source would be useful.
Remote locations tend to be neglected and adjustment of belt cleaning equipment likely to be infrequent. Once a cleaning device is out of adjustment or cleaning pressure drop off occurs, carry back of material is experienced, with debris then falling off along the length of the return run. Inevitably this has to be cleaned up before costly damage occurs to return rollers and belt which increases operating costs for the user.
Further uses of the proposed invention could be accommodated by the use of a pump producing a greater quantity and pressure of hydraulic fluid. This increase of power could be used to provide an automatically interlocked power source to hydraulically drive rotary cleaning brushes, diverting ploughs, diverting plates within the head chute, band plates, belt steering systems and many other devices fitted to conveyor belt systems. To assist the flow of materials down a chute increases in fluid power could be used to power an hydraulic vibrator attached to the chute to induce vibrational forces. The device would be automatically interlocked with the movement of the conveyor. Little maintenance would be required as lubrication will be provided by the flow of oil and would also dissipate any heat generated.
Control of the volume of fluid transmitted may be provided by any suitable method, such as variable output pump, control valve or restrictor. Speed control would be advantageous for a rotary cleaner as its wear rate depends in part on its rotational speed. This readily available control of the brush speed would mean that the cleaner could be easily optimised to suit the conditions that exist on the belt to which it is applied. Hydraulic pressure could also be used to maintain the brush or rotary scraper in contact with the belt surface at a constant cleaning pressure.
A known type of rotary brush cleaner is driven directly from the motion of a roller engaging the upper surface of the return belt. This type of device uses a counterweight acting around the drive/pivot centre to urge the rotary brush into contact with the belt surface and to provide self adjustment. By attaching a pump to the drive roller or brush shaft, hydraulic pressure could be generated to actuators which would provide self adjustment and a constant pre-determined pressure. The length or size of such a device could be reduced by as much as 50% to make installation easier.
The aforementioned methods of adjusting belt scrapers/cleaners such as manual adjustment by screw or bolt, springs, counterweights, rubber torsion springs and air springs/air cylinders all maintain the cleaning pressure even when the conveyor is stationary. This puts unnecessary strain on the components of the belt cleaner at shut down periods. It allows springs to settle in a position and air cylinders to stick due to lack of movement.
The use of an hydraulic pump driven by the motion of the belt allows the belt scraper/cleaner to relax from the belt when the conveyor is stationary. When the pressure drops to the actuators the weight of the cleaner forces the oil back through the pump to the reservoir. This tends to dislodge any material that has built up around the cleaner and any dust around the mechanism.
If a conveyor runs empty for any period of time the scraper/cleaner is still maintained at pressure against the belt surface. This causes unnecessary wear to both belt cover and cleaner element. The proposed method of using the motion of the conveyor belt system to drive a pump would allow the installation of a pump under the troughed section of the conveyor belt. When the belt is in motion without its load of material, the pump would be arranged so that frictional engagement with the pump drive roller does not take place and pressure is therefore not generated, allowing the cleaner to relax from the belt surface. When the conveyor has material being transported, the weight of this material moves the belt into contact with the pump roller and pressurises the cleaner against the belt. This method will increases the life of the belt and the cleaner element.
A further method of relaxing the scraper/cleaner when the conveyor system is running without its load of material, could be a achieved by the use of a diverter valve. A pump could be attached to an existing roller in the conveyor system and produce pressure when the belt is running. The pressure is piped to a diverter valve which is normally closed, allowing the pump to relieve oil pressure back to the reservoir. In this valve position, fluid is allowed to return from the large area of the cylinder through the valve and back to the reservoir, which relaxes the scraper/cleaner. The valve is suspended above the belt and a vertical lever arm is swung by the carried material which opens the valve. This second position of the valve diverts fluids to the large area of the cylinder and actuates the scraper/cleaner against the belt. When the conveyor is not in motion the weight of the cleaner forces fluid through the valve, to exit back to the reservoir. If the conveyor was to stop while still loaded with material the valve would be in its second position, the weight of the cleaner would force oil back to the reservoir by exiting the valve via pressure port, forcing oil through the pump and back to the reservoir.
Mechanical joints in an endless conveyor are a particular problem in that the scraper/cleaner is impacted at high speed as the raised joint passes through the scraper/cleaner. The joint can be damaged by this impact creating costly repairs and downtime. The scraper/cleaner wearing edge can also be damaged by these repetitive blows, tearing lumps out of the blade edge. This allows small particles of material to pass through the scraper/cleaner.
The proposed method of hydraulically adjusting the scraper/cleaner does provide a shock absorbing feature. When the blade is hit by the belt joint the fluid in the cylinder cushions the blow and forces oil back through the pump to the reservoir by overcoming the pressure in the circuit. When the joint has passed through the scraper/cleaner the actuators instantly reapply the said scraper/cleaner.
The proposed hydraulic adjusting system can be arranged so that the scraper/cleaner can be pressurised or relaxed away from the belt surface when a joint approaches and reapplied after the joint has passed over the scraper/cleaner unhindered.
Double acting cylinders can be used in conjunction with a two position, four port directional valve. When the valve is in its normal position of operation, flow from the pump enters the valve and exits to the large area of the actuators, lifting the scraper/cleaner into contact with the belt surface at a constant force. Fluid in the small area of the actuator (piston rod end) is forced back through the valve and exits by a separate line to the reservoir. When the spool of the valve is operated, the flow of oil inside the valve is reversed. Pressure is then applied to the small area of the actuator forcing oil out of the large area which exits the valve by the said separate line to the reservoir.
When the conveyor system stops pressure is not generated and the weight of the scraper/cleaner forces oil through the pump and back to the reservoir. This method pressurises the scraper from the belt surface as the joint approaches and reapplies pressure when the joint has passed through unhindered.
The two position valve would be of a type that has a spring return to its normal operating position. When the spool of the valve is depressed to reverse the flow it is maintained in this reverse flow position for an adjustable period of time. The valve is then allowed to return slowly to its normal operating position. This ability to adjust the rate of return of the valve would allow the joint to pass over the scraper/cleaner unhindered and to reapply pressure to the scraper/cleaner once the joint has passed.
The adjustable rate of return of the valve to its normal position would allow the same valve to be fitted to any speed of belt and its fitting in any convenient location. The spool of the valve could be operated electrically by a solenoid but is preferably operated by the raised joint which is generally proud of the belt surface.
A roller/lever could be positioned close to the belt surface and actuated as the joint passes over or under the said roller/lever. The lever would operate the spool of the valve and be locked in that reverse flow position for an adjustable period of time.
When the set time has lapsed, the valve returns to its normal position and fluid then applied to the large area of the actuator, reapplying the scraper/cleaner at a constant force against the belt. The same pressure can be applied to both ends of the double acting cylinders due to the weight of the scraper/cleaner assisting the pressure applied to the piston rod end and also because the large area of the piston is open to return.
If a vulcanised joint or a damaged section of belt is required to pass unhindered over a scraper/cleaner a small projection could be clipped or fastened to the belt surface to actuate the spool of the said valve.
A simpler method could be used whereby a similar valve with a mechanical time delay is used, but instead of applying pressure to the piston rod end of the cylinder, the valve when operated closes off the pressure from the pump and allows said pump to relieve. This allows fluid in the large area of the cylinder to pass through the valve and back to the reservoir, the weight of the scraper/cleaner forcing the oil back to the reservoir without the need of pressure being applied to the piston rod end of the cylinders. Double acting cylinders could be used with the piston rod end open to atmosphere. When the required time has lapsed, the valve spool returns to its normal position and reapplied pressure to the large area of the cylinders and closes the return line.
This method of pressurising or relaxing the scraper/cleaner from the belt surface when a joint or other obstruction is approaching the scraper/cleaner, could also be used in a compressed air operated system with equal effect.
Belt speed switches are fitted to conveyors to remove power from the conveyor in case of belt slip. The proposed hydraulic system could also act as a speed indicator by the use of a pressure switch. If the speed of the belt decreases the hydraulic pump produces less volume of fluid and the pressure in the circuit would decrease. The pressure switch in the circuit would detect this pressure drop and if connected to the emergency stop circuit would remove power to the conveyor.
The pressure switch would serve a dual purpose as it would eliminate the need of a belt speed switch and protect the hydraulic system in the case of a leak. Should a leak develop in the system and the reservoir run dry, the pressure in the circuit would drop and the pressure switch cause the removal of power to the conveyor system.
Scoop type traction couplings are used to transmit power between the motor and the conveyor driving drum. Hydraulic pressure is created within these couplings and would provide a convenient source of hydraulic pressure to tension various devices such as belt scrapers. A tapping could be taken from the coupling and if necessary the pressure reduced by a valve. Again hydraulic pressure would only be created when the conveyor is in motion and would therefore provide an automatically interlocked source of energy to adjust belt cleaning devices.
The hydraulic power take off from an endless conveyor system or from components or other devices fitted to the conveyor provides a self contained and automatically interlocked power source which can be utilised to self adjust wearing components in the conveyor system whilst maintaining a constant force. The device when applied to scraper/cleaner can reduce wear on the belt surface and the scraper/cleaner blade and work automatically with the belt movement.
The invention also seeks to provide a variable amount of power from the linear or rotary motion of the conveyor belt or other devices within the conveyor system.
By using the rotary motion of an existing roller or by introducing a roller to engage frictionally with any of the belt surfaces or edges, or by utilising the motion of a rotary brush or a motor used for other purposes or any other rotary equipment used or retrofitted to a conveyor, hydraulic pressure can be generated in remote locations where electricity or compressed air is unavailable or financially unviable. Its use would reduce maintenance requirements and capital expenditure. Mounted to the said rotating roller or rotary component by any suitable means, an hydraulic pump will in turn be rotated at a similar speed. The resulting fluid at pressure would be transmitted by hoses or pipes to actuators, thereby providing power to drive or tension any device that can be operated by fluid movement at pressure.
In its simplest form a low volume, low pressure pump with an integral reservoir is turned at low speed by a roller engaging any surface or edge of the conveyor belt. Fluid would be pumped to the actuators via an adjustable relief valve.
As in the case of belt cleaning devices very little movement of the actuators will take place, fluid would be circulated at the desired pressure through the relief valve and back to the reservoir whilst maintaining pressure to the cleaner.
When wears takes place on the cleaning device, pressure in the circuit will automatically keep tension on the cleaning device, ensuring self adjustment throughout its life at a constant pre-determined cleaning pressure.
Control of the fluid output may be achieved by increasing or decreasing the diameter of the roller frictionally engaged with the belt or by the use of gears or pulleys and belts that link the roller to the pump.
Regardless of the means adopted to obtain drive to the pump, no separate or dedicated power source is required. The necessary power input is therefore derived (directly or indirectly) from any convenient source of energy already available within the endless conveyor belt system.